Peter Xu deb4c93a98 mm/khugepaged: don't recycle vma pgtable if uffd-wp registered
When we're trying to collapse a 2M huge shmem page, don't retract pgtable
pmd page if it's registered with uffd-wp, because that pgtable could have
pte markers installed.  Recycling of that pgtable means we'll lose the pte
markers.  That could cause data loss for an uffd-wp enabled application on
shmem.

Instead of disabling khugepaged on these files, simply skip retracting
these special VMAs, then the page cache can still be merged into a huge
thp, and other mm/vma can still map the range of file with a huge thp when
proper.

Note that checking VM_UFFD_WP needs to be done with mmap_sem held for
write, that avoids race like:

         khugepaged                             user thread
         ==========                             ===========
     check VM_UFFD_WP, not set
                                       UFFDIO_REGISTER with uffd-wp on shmem
                                       wr-protect some pages (install markers)
     take mmap_sem write lock
     erase pmd and free pmd page
      --> pte markers are dropped unnoticed!

Link: https://lkml.kernel.org/r/20220405014921.14994-1-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: "Kirill A . Shutemov" <kirill@shutemov.name>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Nadav Amit <nadav.amit@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-05-13 07:20:11 -07:00
..
2021-05-05 11:27:24 -07:00
2022-03-24 19:06:45 -07:00
2022-03-22 15:57:01 -07:00
2022-05-13 07:20:09 -07:00
2022-05-13 07:20:09 -07:00
2022-02-14 19:51:47 +01:00
2022-05-13 07:20:09 -07:00
2022-01-15 16:30:28 +02:00
2022-03-23 18:03:08 -07:00
2022-05-13 07:20:05 -07:00
2022-05-13 07:20:09 -07:00
2022-03-22 17:03:12 -07:00
2022-03-24 19:06:44 -07:00
2022-01-23 06:20:44 +02:00
2021-05-07 00:26:35 -07:00
2022-04-01 14:40:42 -04:00
2022-03-22 18:26:56 -07:00
2022-05-09 18:20:47 -07:00
2022-04-28 23:16:00 -07:00
2022-04-28 23:16:16 -07:00
2022-01-15 16:30:31 +02:00
2022-05-09 18:20:47 -07:00